Arteriovenous access valve system and process

ABSTRACT

An arteriovenous graft system is described. The arteriovenous graft system includes an arteriovenous graft that is well suited for use during hemodialysis. In order to minimize or prevent arterial steal, at least one valve device is positioned at the arterial end of the arteriovenous graft. In one embodiment, a subcutaneous arteriovenous graft system is described. The system includes an arteriovenous graft having an arterial end and an opposite venous end with a first valve device positioned at the arterial end of the arteriovenous graft and a second valve device positioned at the venous end of the arteriovenous graft. The system also includes an actuator having an accumulator. The actuator is in communication with both the first valve device and the second valve device and is configured to cause each valve device to open or close simultaneously. The accumulator assists in maintaining a generally constant pressure when the actuator causes each valve device to close.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 11/807,479, filed May 29, 2007.

BACKGROUND

The function of kidneys, which are glandular organs located in the upperabdominal cavity of vertebrates, is to filter blood and remove wasteproducts. Specifically, kidneys separate water and waste products ofmetabolism from blood and excrete them as urine through the bladder.Chronic renal failure is a disease of the kidney in which the kidneyfunction breaks down and is no longer able to filter blood and removewaste substances. Should certain toxic waste substances not be removedfrom the blood, the toxic substances may increase to lethalconcentrations within the body.

Hemodialysis is a life-sustaining treatment for patients who have renalfailure. Hemodialysis is a process whereby the patient's blood isfiltered and toxins are removed using an extracorporeal dialysismachine. For hemodialysis to be effective, large volumes of blood mustbe removed rapidly from the patient's body, passed through the dialysismachine, and returned to the patient. A number of operations have beendeveloped to provide access to the circulation system of a patient suchthat patients may be connected to the dialysis machine.

For example, the most commonly performed hemodialysis access operationis a subcutaneous placement of an arteriovenous graft, which is madefrom a biocompatible tube. The biocompatible tube can be made of, forinstance, a fluoropolymer such as polytetrafluoroethylene. One end ofthe tube is connected to an artery while the other end is connected to avein. The arteriovenous graft is typically placed either in the leg orarm of a patient.

Blood flows from the artery, through the graft and into the vein. Toconnect the patient to a dialysis machine, two large hypodermic needlesare inserted through the skin and into the graft. Blood is removed fromthe patient through one needle, circulated through the dialysis machine,and returned to the patient through the second needle. Typically,patients undergo hemodialysis approximately four hours a day, three daysa week.

Various problems, however, have been experienced with the use of anarteriovenous graft. For example, arterial steal occurs when excessiveblood flow through the arteriovenous graft “steals” blood from thedistal arterial bed. Arterial steal can prevent the proper supply ofblood from reaching the extremity of a patient.

Various other complications can also occur. For instance, the bloodflowing through the arteriovenous graft can often reach turbulent flowrates. This stream of fast moving blood then exits the arteriovenousgraft and contacts the vein connected to the graft. This collisionbetween the flow of blood and the vein may cause the development ofmyointimal hyperplasia which leads to the thickening of the vein wallsand a narrowing of the vessel. As the vein narrows, flow through thearteriovenous graft decreases and blood within the graft may ultimatelyclot.

The cessation of blood flow through the graft caused by clot formationis known as graft thrombosis. Numerous techniques and medications havebeen studied in attempts to block the development of the scar tissue.Graft thrombosis, however, continues to remain a reoccurringcomplication associated with the use of arteriovenous grafts.

In view of the above drawbacks, a need currently exists in the art foran arteriovenous graft that can prevent and minimize arterial steal andgraft thrombosis. A process for using an arteriovenous graft inminimizing arterial steal and graft thrombosis is also needed.

SUMMARY OF THE INVENTION

In general, the present invention is directed to subcutaneousarteriovenous graft systems and to processes for using the arteriovenousgraft systems in a manner that eliminates or at least reduces arterialsteal and graft thrombosis. In one embodiment, for instance, the systemincludes an arteriovenous graft having an arterial end and an oppositevenous end. The arterial end is configured to be connected to an arteryto form an arterial anastomosis, while the venous end is configured tobe connected to a vein to form a venous anastomosis.

In accordance with the present invention, the system includes at leastone valve device positioned at the arterial end of the arteriovenousgraft. In one embodiment, for instance, the valve device comprises aninflatable balloon. The inflatable balloon is positioned so as torestrict blood flow through the arteriovenous graft when inflated. Ingeneral, the valve device should be positioned at the arterial end ofthe arteriovenous graft as close as possible to the intersection of thegraft with an artery. For example, the valve device may be positioned soas to restrict blood flow through the arteriovenous graft at a locationthat is less than about 10 mm from the intersection of the arteriovenousgraft and an artery.

The inflatable balloon of the valve device may have an annular shapethat surrounds the arteriovenous graft. The inflatable balloon may alsobe a separate structure or may be integral with the arteriovenous graft.When integral with the arteriovenous graft, the arteriovenous graft mayinclude a multi-layered segment located at the arterial end. Themulti-layered segment may comprise an inner layer and an outer layer.The inner layer constricts the graft when a fluid is fed in between theinner layer and the outer layer. When having an annular shape, theballoon may be surrounded by a rigid collar that serves to assist theballoon in constricting the graft.

In an alternative embodiment, the valve device may include an innersleeve and an outer sleeve. The inner sleeve may be attached to theouter sleeve except for over a discrete area. The discrete area can bein fluid communication with a fluid delivery device. When a fluid is fedto the discrete area, fluid is fed in between the inner sleeve and theouter sleeve causing the discrete area of the inner sleeve to inflate.In this embodiment, the discrete area, instead of surrounding thearteriovenous graft, can be circular or substantially circular in shape.When inflated, the discrete area forms a spherically shaped or asubstantially spherically shaped balloon. In one embodiment, forinstance, the outer sleeve may be more rigid than the inner sleeve.Thus, when the inner sleeve is inflated, the outer sleeve maintains itsshape. In this embodiment, the balloon may be integral with thearteriovenous graft. Alternatively, the arteriovenous graft may bepositioned within the inner sleeve.

In order to inflate and deflate the balloon, in one embodiment, thevalve device can further include an injection port in fluidcommunication with the inflatable balloon. The injection port defines adiaphragm configured to receive a hypodermic needle for injecting fluidinto or withdrawing fluid from the balloon. Of particular advantage, theinjection port may also be subcutaneously implanted.

In an alternative embodiment, the inflatable balloon may be positionedin operative association with a piston. In this embodiment, when theballoon is inflated, the balloon forces the piston either towards oraway from the arteriovenous graft for opening or closing the valvedevice.

When the valve device contains a piston, the valve device can includevarious configurations. Further, the piston can be used to inflate aballoon as described above or can be used to activate any other suitablestructure configured to open and close the arteriovenous graft. In fact,in one embodiment, the piston itself may be used to open and close thegraft.

In one embodiment, for example, the valve device may comprise amagnetically activated piston. In this embodiment, when a magnetic fieldis placed in close proximity to the valve device, the piston is movedfor either opening or closing the valve device. For example, in oneembodiment, placing a magnetic field in close proximity to the valvedevice opens the device which normally remains closed.

In one particular embodiment, the magnetically activated piston may beactivated when exposed to a changing magnetic field, such as a pulsingmagnetic field. In this embodiment, the valve device may include a coilmember configured to convert a changing magnetic field into an electriccurrent. The coil member is in communication with a solenoid. Thesolenoid is configured to move the piston and open or close the valvedevice when electric current is received from the coil member.

In an alternative embodiment, the valve device may include a piston thatis biased towards a closed position. For example, a spring or otherstructure may apply a biasing force against the piston that maintainsthe piston in the closed position. In order to move the piston, thepiston can be in operative association with a lever arm. When a magneticfield is placed in close proximity to the valve device, the lever armmay be configured to move causing the piston to move and open the valvedevice. In this embodiment, for instance, the piston may be in fluidcommunication with an inflatable balloon as described above. When thepiston is moved into an open position, a fluid flows out of the balloonfor deflating the balloon. When the piston is placed in the closedposition, on the other hand, the fluid can be forced into the balloonfor inflating the balloon.

In one embodiment, the arteriovenous graft system further includes asecond valve device positioned at the venous end of the arteriovenousgraft. The second valve device may be any suitable valve device asdescribed above. The second valve device, for instance, may be identicalto the first valve device or, alternatively, may be different.

The second valve device may be actuated using any suitable actuator. Forinstance, as described above, in one embodiment, the second valve devicemay include an inflatable balloon that is in fluid communication with aninjection port.

Alternatively, the second valve device may comprise an inflatableballoon that is in communication with a piston as described above.

In still another embodiment of the present disclosure, the subcutaneousarteriovenous graft system includes a first valve device positioned atthe arterial end of the arteriovenous graft, a second valve devicepositioned at the venous end of the arteriovenous graft and a singleactuator in communication with both the first valve device and thesecond valve device. The actuator is configured to open and close thevalve devices simultaneously. The actuator may comprise, for instance, afluid injection port, a piston as described above or any other suitabledevice. For instance, the injection port or the piston may be configuredto deliver a fluid to each of the valve devices for inflating anddeflating a balloon that closes and opens the valves respectively.

The second valve device may not be exposed or subjected to the samefluid pressures that are exerted on the first valve device. In thisregard, the first valve device is designed to restrict or stop fluidflow at relatively high pressures. The second valve device, however, maybe a low pressure valve device. In one embodiment, for instance, thesecond valve device may be a check valve positioned at the venous end ofthe arteriovenous graft. For example, the second valve device may beformed integral with the arteriovenous graft and may be formed from amembrane that allows fluid flow from the arteriovenous graft and into anadjoining vein but prevents fluid flow from the vein into thearteriovenous graft.

In an alternative embodiment, the check valve may comprise a pair ofopposing and overlapping flaps positioned within the arteriovenousgraft. The flaps can be integral with the graft or can be attached tothe arteriovenous graft on opposing sides. For instance, the flaps canbe attached to the graft using sutures or through a welding process. Inorder to prevent leakage, the check valve can further include edge sealsthat are positioned on opposing sides of each flap. The edge seals cancreate a seal with the radial wall of the arteriovenous graft.

The arteriovenous graft of the present invention is used forhemodialysis. During hemodialysis, two hypodermic needles are insertedinto the arteriovenous graft. Blood is removed from the graft using oneneedle, circulated through a dialysis machine, and returned to thearteriovenous graft through the second needle. When hemodialysis is notbeing conducted, however, the valve devices of the present invention maybe activated in order to minimize arterial steal and prevent thrombosisof the graft.

For example, in one embodiment of the present invention, when thearteriovenous graft system only includes a single valve device at thearterial end, after hemodialysis has ended, the valve device is closedthus preventing blood flow through the graft. After the valve device isclosed, a blood compatible fluid may be injected into the graft using ahypodermic needle. As used herein, a blood compatible fluid refers toany fluid that is biocompatible with the circulation system.

For example, in one embodiment, the blood compatible fluid is aheparinized saline solution. The saline solution is used to flush thegraft after the valve device is closed in order to remove blood from thegraft.

In another embodiment, after hemodialysis, the valve device is partiallyclosed to a first position thereby constricting the arteriovenous graftand reducing blood flow through the graft. The patient is then monitoredover a period of time, such as days or weeks, and the valve device maybe selectively opened or closed from the first position until arterialsteal is minimized. In this embodiment, the valve device is closed anamount sufficient to reduce blood flow through the graft without slowingthe blood flow to a point where blood clots may form.

As described above, in another embodiment of the present invention, thearteriovenous graft system includes a first valve device at the arterialend and a second valve device at the venous end. In this embodiment,after hemodialysis has ended, the first valve device at the arterial endis closed thereby preventing blood flow through the graft. A hypodermicneedle then flushes the graft with a blood compatible fluid evacuatingall blood from the graft. After the graft has been flushed with theblood compatible fluid, the second valve device is then closed and thehypodermic needle is removed from the graft.

When the arteriovenous graft system contains first and second valvedevices that are controlled by a single actuator, in one embodiment, thevalve devices are opened so that there is blood flow through the graft.Two hypodermic needles are inserted into the graft and the blood iscirculated through a dialysis machine. After hemodialysis has ended, theactuator is used to close both valve devices simultaneously. Thearteriovenous graft can then be flushed. For instance, a fluid can beinjected and removed from the graft using one or more hypodermicneedles.

In still another embodiment of the present disclosure, a subcutaneousarteriovenous graft system is described. The system includes anarteriovenous graft having an arterial end and an opposite venous endwith a first valve device positioned at the arterial end of thearteriovenous graft and a second valve device positioned at the venousend of the arteriovenous graft. The system also includes an actuatorhaving an accumulator. The actuator is in communication with both thefirst valve device and the second valve device and is configured tocause each valve device to open or close simultaneously. The accumulatorassists in maintaining a generally constant pressure when the actuatorcauses each valve device to close.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention is set forth inthe specification with reference to the following figures.

FIG. 1 is a side view with cut away portions of a human arm illustratingthe placement of an arteriovenous graft;

FIGS. 2A, 2B and 2C are perspective views of embodiments ofarteriovenous graft systems made in accordance with the presentinvention;

FIG. 3 is a perspective view of one embodiment of a valve device thatmay be used in the arteriovenous graft system of the present invention;

FIG. 4 is a perspective view of another embodiment of a valve devicethat may be used in the arteriovenous graft system of the presentinvention;

FIG. 5 is a perspective view of still another embodiment of anarteriovenous graft system made in accordance with the presentinvention;

FIG. 6 is an unassembled perspective view of one embodiment of a balloonvalve that may be used in accordance with the present disclosure;

FIG. 7 is a cross-sectional view of the valve device illustrated in FIG.6;

FIG. 8 is a cross-sectional view taken along line A-A of the valvedevice shown in FIG. 7;

FIG. 9 is a cross-sectional view of the valve device illustrated in FIG.6 showing the balloon inflated;

FIG. 10 is a perspective view with cut away portions showing anotherembodiment of a valve device that may be used in accordance with thepresent disclosure;

FIG. 11 is a cross-sectional view of the valve device illustrated inFIG. 10;

FIG. 12 is a side view with cut away portions illustrating the valvedevice shown in FIG. 10 in association with a balloon;

FIG. 13 is a cross-sectional view of the valve device illustrated inFIG. 12 illustrating the balloon being deflated;

FIG. 14 is an unassembled perspective view of one embodiment of a checkvalve that may be used in accordance with the present disclosure;

FIG. 15 is a perspective view with cut away portions of the check valveillustrated in FIG. 14;

FIG. 16 is a cross-sectional view of the check valve illustrated in FIG.14;

FIG. 17 is a cross-sectional view taken along line A-A of the checkvalve illustrated in FIG. 16;

FIG. 18 is an alternative embodiment of a check valve that may be usedin accordance with the present disclosure;

FIG. 19 is a perspective view of yet another alternative embodiment ofan arteriovenous graft system in accordance with the present disclosure;

FIG. 20 is a perspective view of yet another alternative embodiment ofan arteriovenous graft system in accordance with the present disclosure;and

FIG. 21A is an exploded view of the actuator illustrated in

FIG. 20; and

FIGS. 21B and 21C are cross-sectional views of the actuator illustratedin FIG. 21A.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made to the embodiments of the invention, one ormore examples of which are set forth below. Each example is provided byway of explanation of the invention, not as a limitation of theinvention. In fact, it will be apparent to those skilled in the art thatvarious modifications and variations may be made in the inventionwithout departing from the scope or spirit of the invention. Forinstance, features illustrated or described as part of one embodimentmay be used in another embodiment to yield a still further embodiment.For example, an arteriovenous graft system may include combinations ofthe valve devices described below. Thus, it is intended that the presentinvention cover such modifications and variations as come within thescope of the appended claims and their equivalents. It is to beunderstood by one of ordinary skill in the art that the presentdiscussion is a description of exemplary embodiments only, and is notintended as limiting the broader aspects of the present invention, whichbroader aspects are embodied in the exemplary construction.

In general, the present invention is directed to an implantablearteriovenous graft system that may be used in carrying out hemodialysistreatments. Although the following description will refer to thearteriovenous graft system being implanted into an arm, it should beunderstood that the system may be implanted in any suitable location ofthe body. For example, in other embodiments, the arteriovenous graftsystem may be implanted into a leg.

In addition to being well suited for carrying out hemodialysis, thearteriovenous graft system of the present invention also prevents orminimizes arterial steal and graft thrombosis. In particular, thearteriovenous graft system is designed to prevent or minimize blood flowthrough the graft when hemodialysis is not occurring.

Referring to FIG. 1, for purposes of explanation, a right arm 10 of apatient is shown. Selected arteries (shown as dotted pathways) areillustrated in conjunction with selected veins (shown as dark pathways).An arteriovenous graft 12 is shown connected at one end to an artery andat an opposite end to a vein. In particular, the arteriovenous graft 12is connected to the brachial artery 14 and to the cephalic vein 16.

The arteriovenous graft 12 is made from any suitable biocompatiblematerial. For example, in one embodiment, the graft is made from afluoropolymer, such as polytetrafluoroethylene, which is commerciallyavailable as GORTEX™ from the W. L. Gore Company.

Referring to FIGS. 2A and 2B, one embodiment of an arteriovenous graftsystem made in accordance with the present invention is shown includingan arteriovenous graft 12. As illustrated, the arteriovenous graft 12 isconnected to an artery 14 and to a vein 16. In order to carry outhemodialysis, a first hypodermic needle 18 is inserted through the skinand into the arteriovenous graft 12. Blood is removed from thearteriovenous graft 12 through the needle and into a dialysis machine20. In the dialysis machine, waste materials are removed from the blood.After circulating through the dialysis machine 20, the blood is then fedback into the arteriovenous graft 12 through a second hypodermic needle22.

In accordance with the present invention, the arteriovenous graft systemas shown in FIGS. 2A and 2B further includes at least a first valvedevice generally 24 positioned at the arterial end of the arteriovenousgraft 12. Optionally, the arteriovenous graft system can further includea second valve device generally 26 positioned at the venous end of thearteriovenous graft. The valve devices 24 and 26 are in an open positionduring normal hemodialysis as shown in FIG. 2A.

When hemodialysis has ended, however, the valve devices 24 and 26 aremoved to a closed position in order to prevent blood flow through thearteriovenous graft. In this manner, arterial steal is either eliminatedor reduced. Further, by reducing turbulent blood flow through thearteriovenous graft, graft thrombosis is also prevented.

In addition to minimizing arterial steal and preventing graftthrombosis, the system and the process of the present invention alsooffer various other advantages. For example, reducing or stopping bloodflow through the arteriovenous graft when hemodialysis is not occurringalso prevents the graft from bleeding when the hypodermic needles usedto carry out hemodialysis are removed from the graft. Hypodermic needlesas shown in FIG. 2B, for instance, usually have a relatively largediameter or gauge. Thus, when the needles are removed from a graft,bleeding can occur where the needles have previously been. Needle holebleeding through the graft can result in the formation of scar tissueand graft pseudoaneurisms. These complications, however, may beprevented through the use of the system of the present invention.

In the embodiment shown in FIG. 2A, the valve devices 26 and 24 eachinclude an inflatable balloon 28 and 30. When inflated, the balloons 28and 30 constrict the arteriovenous graft 12 for reducing or eliminatingblood flow through the graft.

As shown in FIG. 2A, the inflatable balloons 28 and 30, in thisembodiment, have an annular shape that surround the arteriovenous graft12. As shown, each of the inflatable balloons 28 and 30 are alsosurrounded by a rigid collar 32 and 34. Each collar 32 and 34 may beincluded in the system in order to maintain each of the balloons 28 and30 in the proper position. Further, the collars 32 and 34 also serve tobias the balloon towards the arteriovenous graft 12 when inflated. Eachcollar 32 and 34 may be made from any rigid biocompatible material. Forexample, the collars 32 and 34 may be made from a metal, such astitanium, or a plastic material.

Each annular balloon 28 and 30 may be a separate structure from thearteriovenous graft 12 or may be integral with the graft. When integralwith the graft, for instance, the graft may include a multi-layeredsegment where each of the valve devices is to be located. For example,within the multi-layered segment, the arteriovenous graft 12 may includean outer rigid layer and an inner luminal layer. The balloon 28 and 30may be formed in between the outer layer and the inner layer. Inparticular, when a fluid is injected in between the inner and outerlayers, the inner layer may expand and constrict the lumen. See FIG. 2C.

In addition to having an annular shape, it should be understood thateach balloon 28 and 30 may have any shape sufficient to constrict thearteriovenous graft when inflated. For instance, in another embodiment,each balloon 28 and 30 may be located on one side of the graft 12. Wheninflated, the balloons 28 and 30 force opposite sides of the grafttogether.

For example, referring to FIGS. 6 through 8, an alternative embodimentof a valve device containing an inflatable balloon is shown. Asillustrated in FIG. 6, the valve device includes an inner sleeve 110positioned within an outer sleeve 112. The inner sleeve can be attachedor bonded to the outer sleeve at all locations except over a discretearea 114. As shown in FIGS. 7 and 8, the discrete area 114 is positionedopposite a fluid passageway 116. The fluid passageway 116 is placed incommunication with a fluid delivery device. When fluid is forced throughthe fluid passageway 116, the fluid causes the discrete area 114 toinflate and form a balloon as shown in FIG. 9.

The inner and outer sleeves can be made from various materials and canbe formed using various techniques. In one embodiment, for instance, theinner and outer sleeves can be injection molded and bonded together. Forexample, both the inner sleeve and the outer sleeve may be made from asuitable elastomer, such as a silicone elastomer. The outer sleeve 112can be made more rigid than the inner sleeve 110 so that the outersleeve preserves its shape when the discrete area 114 is inflated. Theouter sleeve 112 can be made more rigid by having a greater thickness orby being made from a stiffer material, such as a material that has ahigher durometer in comparison to the material used to form the innersleeve.

In order to attach the inner sleeve 110 to the outer sleeve 112, anysuitable technique may be used. For example, in one embodiment, anadhesive material, such as an adhesive material containing a siliconeelastomer may be used to bond the two layers together. In otherembodiments, the two layers may bond together during the moldingprocess.

As shown in FIG. 8, in one embodiment, the discrete area 114 may have athickness that is less than the thickness of the remainder of the innersleeve 110.

For instance, the discrete area 114 may have a thickness of less thanabout 0.015 inches. As shown in FIG. 6, in one embodiment, the discretearea 114 may have a circular or a substantially circular shape. Byhaving a substantially circular shape, the discrete area expandsuniformly and inflates evenly across its plane during inflation, thusminimizing stress on the material. Once inflated as shown in FIG. 9, thediscrete area 114 can have a spherical or substantially spherical shape.The inflated shape can compress the arteriovenous graft and preventleakage. The substantially spherical shape also allows the balloon to beinflated to a size and pressure which can assure constriction andsealing of a 200 mmHg pressure gradient across the graft. The ballooncan also be designed to be overpressurized by greater than about 30%thus serving as a safety factor. Ultimately, the design is free of bulk,pinch points which minimizes patient discomfort.

The valve device as shown in FIGS. 6 through 9 can be integral with thearteriovenous graft or the arteriovenous graft can fit inside the innersleeve 110. In one embodiment, the inner and outer sleeves can be slitalong the length in order to facilitate installation over a graft. Onceinstalled over a graft, the slit formed in the valve device can beconnected together through thermal bonding, clips or sutures.

In order to inflate the balloons as shown in the figures, in oneembodiment as shown in FIGS. 2A and 2B, each valve device may furtherinclude an injection port 36 and 38. For example, as shown in FIG. 2A,injection port 36 may be in fluid communication with the balloon 28 viaa tubing 40. Similarly, injection port 38 may be in fluid communicationwith the balloon 30 via a tubing 42. Each injection port 36 and 38 maybe configured to be subcutaneously implanted in a patient.

In the embodiment illustrated in FIG. 2A, injection ports 36 and 38 eachinclude a diaphragm 44 and 46 positioned on one side of a housing 48 and50. The housings 48 and 50 may be made from any suitable rigid andbiocompatible material. For example, each housing may be made from ametal, such as titanium.

Each diaphragm 44 and 46, on the other hand, may be made from a materialcapable of receiving the tip of a hypodermic needle. For example, eachdiaphragm 44 and 46 may be made from an elastomeric film, such as asilicone membrane.

As shown particularly in FIG. 2B, in order to inflate or deflate theballoons 28 and 30, hypodermic needles 52 and 54 may inject a fluid intoeach of the injection ports 36 and 38 through the diaphragms 44 and 46.The fluid travels from the injection ports 36 and 38 through the tubing40 and 42 and into each respective balloon 28 and 30. Similarly, thehypodermic needles 52 and 54 may also be used to withdraw fluid from theballoons 28 and 30.

As shown in FIG. 2B, once inflated, the balloons 28 and 30 constrict thearteriovenous graft 12 at the arterial end and at the venous end. Thefluid used to inflate the balloons 28 and 30 may vary depending upon theparticular application. The fluid may be, for instance, a gas or liquid.In one embodiment, for instance, a saline solution may be injected intothe injection ports 36 and 38 for inflating the balloons. In oneembodiment, it may take from about 2 ccs to about 6 ccs of fluid totransition each balloon valve 28 and 30 from an open position to aclosed position.

When closed, each valve device should be capable of maintaining itsposition when exposed to systolic pressure. For example, systolicpressures in arteries may be greater than about 250 mmHg, such as fromabout 170 mmHg to about 270 mmHg.

In addition to withstanding relatively high fluid pressures, each of thevalve devices 24 and 26 should also be constructed so that the valvedevices can constrict the arteriovenous graft as close as possible tothe intersection of the graft with the artery 14 and the vein 16. Forexample, the first valve device 24, in one embodiment, constricts thearteriovenous graft at a distance of from about 5 mm from the arterialanastomosis, such as no greater than about 20 mm from the arterialanastomosis. The position of the second valve device 26 in relation tothe venous anastomosis may also be within the above defined limits.

The methods for using the arteriovenous graft system of the presentinvention will now be discussed in relation to a system that contains asingle valve device positioned at the arterial end of the graft and asystem that contains two valve devices as shown in FIGS. 2A and 2B.

When the arteriovenous graft system of the present invention contains asingle valve device positioned at the arterial end, in one embodiment,the valve device may be positioned so as to constrict blood flow throughthe graft when hemodialysis is not occurring. In this embodiment,arterial steal is not being completely prevented but is being minimized.In particular, the single valve device constricts the graft so thatblood flow through the graft continues without clotting but is at areduced flow rate.

In this embodiment, the patient's condition may need to be monitoredover a period of time, such as days or weeks, and the valve device maybe adjusted in order to minimize arterial steal without causing acomplete blood stoppage. For instance, over several days or weeks, thearteriovenous graft of the patient may be monitored and the valve devicemay be adjusted so as to gradually increase or decrease the narrowing ofthe arteriovenous graft. The ultimate position of the valve will varydepending upon the patient and the location of the arteriovenous graft.

In an alternative embodiment, the single valve device may be used tocompletely close off the arteriovenous graft 12 at the arterial end. Inthis embodiment, during hemodialysis, the valve device 24 is in the openposition and the arteriovenous graft 12 is cannulated with the twodialysis needles 18 and 22 as shown in FIG. 2A. Upon completion ofdialysis, a fluid is injected into the injection port 36 of the firstvalve device causing the balloon 28 to inflate thereby closing the valvedevice and eliminating arterial blood flow through the graft. After thevalve device is closed, a blood compatible fluid is then injected intothe arteriovenous graft 12 through, for instance, a dialysis needle toflush any residual blood out of the graft. The blood compatible fluidcan be, for instance, heparinized saline. The residual blood is flushedout of the graft in order to prevent any clotting.

In this embodiment, some residual saline remains in the graft untilhemodialysis is once again conducted on the patient. This embodimentshould only be used when it is determined that substantially no bloodfrom the vein 16 will flow into the graft once valve device 24 isclosed.

In order to prevent any blood flowing from the vein 16 back into thearteriovenous graft 12 after the first valve device 24 has been closed,in one embodiment of the present invention as shown particularly inFIGS. 2A and 2B, the arteriovenous graft system can include the secondvalve device 26. In this embodiment, the process as described above isrepeated. After the arteriovenous graft 12 is flushed with a bloodcompatible fluid, however, a fluid is injected into the injection port38 of the second valve device 26 which causes the second valve device toclose.

In addition to the valve devices as illustrated in FIGS. 2A and 2B, inother embodiments, other valve devices may also be utilized in thesystem of the present invention. For example, referring to FIG. 4,another embodiment of a valve device generally 60 is shown incommunication with an arteriovenous graft 12. In this embodiment, thevalve device 60 includes a fluid chamber 62 in communication with aninjection port 64 similar to the injection ports described above. Asshown, injection port 64 includes a diaphragm 68 configured to receivefluid from a hypodermic needle 70.

The valve device 60 further includes a piston 72 contained within ahousing 74. The piston 72 is positioned below the fluid chamber 62.

In this embodiment, when a fluid is injected from the needle 70 into theinjection port 64, the fluid is forced into the fluid chamber 62 via atube 66. The pressure of the fluid then forces the piston 72 to lowerclosing the valve and constricting flow through the arteriovenous graft12.

Valve device 60 as shown in FIG. 4 may be used in a single valve systemof the present invention or in a double valve system of the presentinvention as illustrated in FIG. 2A.

Referring to FIG. 3, another embodiment of a valve device generally 80that may be used in the arteriovenous graft system of the presentinvention is illustrated. In this embodiment, the valve device 80includes a housing 82 containing a magnetically actuated piston 84.Specifically, the valve device is configured such that the piston 84moves between an open and closed position when the valve device iscontacted with a magnetic field.

In this particular embodiment, the valve device 80 includes a coilmember 86. The coil member 86 is configured to convert a pulsatingmagnetic field into an electric current. As shown, the coil member 86then supplies the electric current to a solenoid 88. Solenoid 88 thenmoves the piston 84 to either open or close the valve device.

In order to activate the valve device 80, a magnetic key 90 is placedclose to the skin of a patient. In this embodiment, the magnetic key 90may be an electromagnet that creates a pulsating magnetic field. Asdescribed above, the pulsating magnetic field is then converted into anelectric current by the coil member 86. The magnetic key 90 may beconfigured either to open or to close the valve device. In oneembodiment, for instance, the valve device 80 may normally be found in aclosed position blocking off the arteriovenous graft 12. When themagnetic key 90, however, is placed adjacent to the patient's skin, thevalve device 80 then opens allowing blood to circulate through thegraft. In other embodiments, however, it should be understood that thevalve device may be configured to close when placed adjacent to themagnetic key 90.

In addition to the valve device 80 as shown in FIG. 3, othermagnetically activated valves may be used in the system of the presentinvention. For example, in another embodiment of the present invention,the valve device may include a piston in operative association with apermanent magnet. A ferrous plate may be positioned on the opposite sideof the arteriovenous graft. Thus, the permanent magnet contained in thepiston is attracted to the ferrous surface for closing off thearteriovenous graft. When a magnet with opposite polarity, however, isplaced adjacent to the valve device, the permanent magnet containedwithin the piston is attracted to the reverse magnetic field causing thevalve to open.

Referring to FIGS. 10 through 13, still another embodiment of amagnetically activated valve device that may be used in accordance withthe present disclosure is shown. In this embodiment, the valve deviceincludes a magnetically activated piston 120 as shown in FIG. 10. Asillustrated, the piston 120 is contained within a housing 122. Thepiston is biased towards a closed position by a spring 124. Inparticular, the spring 124 applies a biasing force to the piston 120.

As shown in FIGS. 10 and 11, the piston is also attached to a lever arm126. The lever arm 126 is attached to a magnet member 128 or amagnetically attractable member 128. In this embodiment, when anexternal key comprising a magnet or an electromagnet is placed adjacentto the member 128, the lever arm 126 moves which in turn causes thepiston to move and open or close the valve.

In the embodiment shown in the figures, the piston 120 is normallybiased in a closed position. When a magnetic key is placed adjacent tothe valve device, the lever arm causes the piston 120 to move and openthe valve device. It should be understood, however, that in otherembodiments the lever arm may be used to close the valve.

The piston 120 as shown in FIG. 10 can be placed in association with anarteriovenous graft in order to open and close the graft. In oneparticular embodiment as shown in FIG. 12, for example, the piston 120can be placed in communication with a balloon valve such as the oneillustrated in FIGS. 6 through 9. In this embodiment, the piston 120 isused as a fluid delivery device that delivers fluid to the balloon.

For instance, referring to FIG. 12, the piston 120 is shown in a closedposition caused by a biasing force being placed against the piston bythe spring 124. When in the closed position, the piston 120 forces afluid through the conduit 130 and in contact against the discrete area114, causing the discrete area to inflate and form a substantiallyspherical shape. When inflated, the discrete area 114 blocks flowthrough the arteriovenous graft.

When it is desired to open the arteriovenous graft for dialysistreatment, for instance, a key comprising a magnet or an electromagnetis placed adjacent to the valve device. Referring to FIG. 13, forinstance, the magnetic or electromagnetic key is placed adjacent to themagnetic member or magnetically attractable member 128 causing the leverarm 126 to pivot or move. The lever arm 126 is attached to a linkingmember 132 that is in turn connected to the piston 120.

When the lever arm 126 is pivoted, the linking member 132 causes thepiston to retract as shown. Fluid contained within the conduit 130 isthereby drawn out of the discrete area 114 causing the balloon todeflate. In this manner, the valve device is opened for allowing bloodflow through the arteriovenous graft. During the dialysis treatment, theexternal magnetic key can be fixed into position to ensure that thevalve device stays open. For instance, the external key can be taped orotherwise attached to the skin of the patient. When the dialysistreatment is concluded, the external magnetic key is removed and thevalve device automatically returns to the closed position.

The fluid that is contained within the valve device may vary dependingupon the particular application and the desired results. In oneembodiment, for instance, a saline solution may be contained within thevalve device.

In the embodiment illustrated in the drawings, the lever arm 126 ismoved based upon an attracting magnetic force. It should be understood,however, that magnetic repulsion can also be used to move the lever armas well.

The valve device as shown in FIGS. 10 through 13 can be designed to berelatively small for being implanted under the skin of a patient. Forinstance, the housing 122 as shown in FIG. 10 can have a diameter lessthan about 3 cm and can have a height of less than about 1 cm.

Using a magnetically actuated valve device as shown in FIGS. 10 through13 can provide various advantages. For instance, because the valvedevice is magnetically actuated, the valve device eliminates the need touse hypodermic needles for transferring liquid into and out of a plenumor port.

In still another embodiment, the valve device as shown in FIGS. 10through 13 may be actuated other than through use of a magnet. Forinstance, in one embodiment, the valve device may include a pump incommunication with a battery. The pump may be turned on and off usingwireless telemetry. In fact, wireless telemetry may also deliver realtime pressure measurements thereby communicating the status of the valvedevice.

Another embodiment of an arteriovenous graft system in accordance withthe present disclosure is illustrated in FIG. 19. Like referencenumerals have been used to identify similar features and elements ofother embodiments. As shown, the system illustrated in FIG. 19 issimilar to the embodiment illustrated in FIG. 2A. As shown, the systemincludes an arteriovenous graft 12 that is connected to an artery 14 atone end and to a vein 16 at an opposite end. In accordance with thepresent disclosure, the system includes a first valve device 24positioned at the arterial end and a second valve device 26 positionedat the venous end of the graft. The first valve device 24 and the secondvalve device 26 are constructed similar to the valve devices illustratedin FIGS. 6-9. It should be understood, however, that any suitable valvedevice can be positioned at either end of the graft. Further, the firstvalve device can be the same or can be different from the second valvedevice.

In the embodiment illustrated in FIG. 19, the first valve device 24 andthe second valve device 26 are both connected to a single actuator 36.The actuator 36 is configured to open and close both valve devicessimultaneously. For example, in the embodiment illustrated, the actuator36 comprises a fluid port that is in communication with the first valvedevice 24 via tubing 40 and is in communication with the second valvedevice 26 via tubing 42. When a fluid is injected or withdrawn from theport 36, both valve devices close or open respectively.

Various benefits and advantages may be realized by only having a singleactuator for both valve devices as shown in FIG. 19. For instance, onlyhaving a single actuator simplifies the system and only requires that asingle actuator be implanted within a patient. Further, in someapplications, there may be advantages to having the valve devices openand close simultaneously.

The actuator 36 as shown in FIG. 19 comprises an injection port. Itshould be understood, however, that any suitable valve actuator may beinstalled within the system. For instance, in an alternative embodiment,the actuator 36 may comprise a piston such as shown in FIGS. 10-13 thatmay be configured to inflate and deflate a balloon contained within thevalve devices. In still another embodiment, the actuator 36 may comprisea solenoid that is configured to electrically open and close the valvedevices.

In order to carry out hemodialysis, a first hypodermic needle 18 and asecond hypodermic needle 22 are shown inserted into the arteriovenousgraft 12. When the valve devices 24 and 26 are open, blood can circulatefrom the graft into the first hypodermic needle 18, through the dialysismachine 20 and back into the graft through the hypodermic needle 22.

In one embodiment, the valve devices 24 and 26 are normally configuredto be in a closed position. In order to open the valve devices andpermit blood flow through the graft, fluid can be removed through theactuator 36 causing the balloons in the valve devices to deflate. Onceboth valve devices are open, the dialysis process can be carried out.

Once a sufficient amount of blood has been circulated through thedialysis machine, fluid can then be inserted into the actuator 36 forsimultaneously closing the valve devices 24 and 26. Closing the valvedevices stops blood flow through the graft. After hemodialysis iscomplete, the graft 12 can be flushed. For instance, a blood compatiblefluid can be circulated through the graft using a single hypodermicneedle or through the use of two hypodermic needles. In one particularembodiment, for instance, one hypodermic needle can be used to insert ablood compatible fluid, such as a saline solution, through the graftwhile a second needle can be used to remove the fluid.

Referring to FIG. 5, another embodiment of an arteriovenous graft systemmade in accordance with the present invention is shown. Like referencenumerals have been used in order to identify similar features andelements of other embodiments. As shown, in this embodiment, thearteriovenous graft system includes a first valve device generally 24 atthe arterial end of the graft similar to the valve device shown in FIGS.2A and 2B. In particular, the first valve device 24 includes a balloon28 that is inflated or deflated using an injection port 36. The balloon28 is for constricting the arteriovenous graft when desired. Asexplained above, the first valve device 24, for most applications, iscapable of maintaining a closed or constricted position on the grafteven when exposed to relatively high fluid pressures. In someembodiments, however, these same pressures are not experienced at thevenous end of the graft.

In this regard, in this embodiment, the arteriovenous graft 12 includesa second valve device generally 100 that may be described as a lowpressure valve device when compared to the first valve device 24.

For example, in one embodiment, the second valve device 100 may be acheck valve that allows fluid flow from the graft 12 into the vein 16but does not permit flow from the vein 16 into the graft 12. In general,any suitable check valve may be used in accordance with the presentinvention.

In the embodiment shown in FIG. 5, the second valve device 100 includesa membrane 102 made from, for instance, a polymeric film that is formedor is connected so as to be integral with the arteriovenous graft 12.The membrane 102 may be, for instance, a flap that allows fluid flow inone direction from the graft 12 into the vein 16. The membrane 102 maybe formed from a single piece of film or may be formed from multiplesegments. For example, in one embodiment, the film can include one ormore slits that permit fluid flow in one direction.

The arteriovenous graft system in FIG. 5 provides various advantages.For example, in the embodiment shown in FIG. 5, only the first valvedevice 24 needs to be manually opened or closed.

In the embodiment shown in FIG. 5, the first valve device is representedas a balloon valve. It should be understood, however, that the firstvalve device may be any of the other valve devices shown and describedabove.

The second valve device 100 as shown in FIG. 5 represents one embodimentof a check valve (a valve that allows flow in one direction) that may beused in accordance with the present disclosure. It should be understood,however, that various other check valves may be used. For instance,referring to FIGS. 14 through 18, another embodiment of a check valvedevice 150 is illustrated. As shown in FIGS. 14 and 15, for instance,the check valve device 150 includes a pair of overlapping flaps 152 and154. The overlapping flaps allow fluid flow only in one direction. Asshown, the opposing flaps 152 and 154 are generally planar and parallel.The flaps can be integral with the arteriovenous graft 156 or can beattached to the graft using any suitable technique. For instance, asshown in FIG. 15, the arteriovenous graft 156 can include a pair ofopposing slits through which the flaps are inserted. The flaps can thenbe attached to the graft 156 by being welded in place or through the useof a biocompatible adhesive. In an alternative embodiment as shown inFIG. 18, sutures 158 can be used in order to attach the flaps to thearteriovenous graft 156.

In addition to the flaps 152 and 154, the check valve device 150 canfurther include edge seals 160, 162, 164 and 166 as shown in FIGS. 16and 17. The edge seals 160, 162, 164 and 166 are positioned on bothsides of each flap and are designed to create a seal with the radialwall of the graft 156. The edge seals are generally located where theflaps are not connected to the graft 156.

The check valve device 150 can be made from any suitable material. Forinstance, the flaps and the edge seals can be made from expanded orunexpanded PTFE, polyurethane and/or silicone. The blood contactingsurfaces may be treated and/or textured to enhance their formation of apseudointima, optimize thrombocompatibility and flow characteristics.

Referring to FIG. 20, another embodiment of an arteriovenous graftsystem in accordance with the present disclosure is illustrated. Again,like reference numerals have been used to identify similar features andelements of other embodiments. The system illustrated in FIG. 20 issimilar to the system illustrated in FIG. 19. The system includes anarteriovenous graft 12 that is connected to an artery 14 at one end andto a vein 16 at an opposite end. The system also includes a first valvedevice 24 positioned at the arterial end and second valve device 26positioned at the venous end of the graft. It should be understood,however, that any suitable valve device can be positioned at either endof the graft. Further, the first valve device can be the same or can bedifferent from the second valve device.

As shown in FIG. 20, the first valve device 24 and second valve device26 are both connected to actuator 200. Actuator includes housing 214.Housing 214 can be made from any suitable rigid and biocompatiblematerial. For example, housing can be made from a metal, such astitanium. Actuator 200 is configured to open or close both valve devicessimultaneously. For example, in the illustrated embodiment, actuator 200is in fluid communication with first valve device 24 via tubing 40connected to first outlet nozzle 218 and is in fluid communication withthe second valve device 26 via tubing 42 connected to second outletnozzle 220. Actuator 200 can be configured to be subcutaneouslyimplanted in a patient.

Referring to FIGS. 21A-C, actuator 200 includes an accumulator 204.While a preferred accumulator is described herein, it should beunderstood that any suitable accumulator can be utilized in connectionwith the present invention. Accumulator 204 is positioned within housing214. Accumulator 204 is an energy storage device which can exertpressure into the arteriovenous graft system of the present invention.

Accumulator 204 can advantageously assist in maintaining a generallyconstant pressure when the actuator 200 causes each valve 24, 26 (asillustrated in FIG. 20) to close. When closed, each valve device shouldbe capable of maintaining its position when exposed to systolicpressure. For example, systolic pressures in arteries may be greaterthan about 250 mmHg, such as from about 170 mmHg to about 270 mmHg.Accumulator 204 includes spring 206 which exerts force against piston208 which can maintain suitable pressure in the arteriovenous graftsystem of the present invention. Liquid is prevented from contactingspring 206 because diaphragm 210 provides a barrier between spring 206and fluid path 212. O-ring 226 can assist in ensuring sealing engagementbetween the diaphragm 210 and housing 214 to prevent fluid from enteringfluid path 212. An accumulator top 222 can maintain the variouscomponents in the housing 214.

Actuator 200 also includes fluid injection port 202. Fluid injectionport 202 can assist in opening and closing first valve device 24 andsecond valve device 26. For example, as shown in FIG. 20, fluidinjection port 202 can be in fluid communication with first valve device24 via tubing 40 and in communication with the second valve device 26via tubing 42.

Turning again to FIGS. 21A-C, fluid injection port 202 includes a septum216 positioned on one side of a housing 214. Septum 216 can be made froma material capable of receiving the tip of a hypodermic needle. Forexample, septum 216 can be made from an elastomeric film, such as asilicone membrane. Septum 216 can be of any suitable thickness. However,septum 216 should be of sufficient thickness to resist pressure from theaccumulator 204 and prevent fluid from unintentionally leaking fromseptum 216. The septum 216 can be held in place in the housing 214 byport top 224.

When fluid is injected or withdrawn through septum 216, both valvedevices 24, 26 open or close respectively. In this regard, accumulator204, which can be positioned adjacent to injection port 202, can storeenergy in spring 206 as a result of the pressure generated from thefluid that is injected. If any of the pressure in the system is lost,spring 206 can release energy through piston 208 to maintain a generallyconstant pressure. As pressure decreases in the system, the spring 206is permitted to expand and piston 208 extends into fluid path 212,maintaining a generally constant pressure. For instance, referring toFIG. 21B, spring 206 is almost fully extended indicating the pressure inthe system is less than that being exerted by the spring 206. Bycontrast, referring to FIG. 21C, the spring 206 is not fully extendedindicating pressure against the accumulator 204 and energy stored inspring 206. Again, however, any suitable accumulator can be used inconnection with the present disclosure.

Various benefits and advantages can be realized by having an actuator200 which includes an accumulator 204 as shown in FIG. 20. For example,air can diffuse through tubing 40, 42 causing a decrease in pressure atvalve devices 24, 26. A concern over such loss in pressure is that valvedevices 24, 26 could open allowing blood to enter graft 12. However, ithas been advantageously discovered that accumulator 204 of the presentdisclosure can prevent such loss in pressure. Because accumulator 204 isincorporated into actuator 200, the system is greatly simplified byrequiring only actuator 200 to be implanted within a patient. However,it should be understood that the accumulator described herein can beutilized in connection with any of the other embodiments of the presentinvention, including embodiments in which more than one actuator isutilized.

Turning again to FIG. 20, in order to carry out hemodialysis, a firsthypodermic needle 18 and a second hypodermic needle 22 are showninserted into the arteriovenous graft 12. As described previously, whenthe valve devices 24 and 26 are open, blood can circulate from the graftinto the first hypodermic needle 18, through the dialysis machine 20 andback into the graft through the hypodermic needle 22.

In one embodiment, the valve devices 24 and 26 are normally configuredto be in a closed position. In this regard, accumulator 204 assists inmaintaining a generally constant pressure when the actuator causes eachvalve device to close.

In order to open the valve devices and permit blood flow through thegraft, fluid can be removed through the actuator 200 causing theballoons in the valve devices to deflate. Once both valve devices areopen, the dialysis process can be carried out.

Once a sufficient amount of blood has been circulated through thedialysis machine 20, fluid can then be inserted into the actuator 200for simultaneously closing the valve devices 24 and 26. Closing thevalve devices stops blood flow through the graft. Again, accumulator 204assists in maintaining a generally constant pressure when the actuatorcauses each valve device to close. After hemodialysis is complete, thegraft 12 can be flushed.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

What is claimed:
 1. A subcutaneous arteriovenous graft systemcomprising: an arteriovenous graft having an arterial end and anopposite venous end; a first valve device positioned at the arterial endof the arteriovenous graft and a second valve device positioned at thevenous end of the arteriovenous graft; and an actuator including ahousing having a first housing portion and a second housing portionspaced apart from the first housing portion, the first housing portionconfigured to receive an accumulator of the actuator and the secondhousing portion configured to receive a fluid injection port of theactuator such that the accumulator is separate from the fluid injectionport, the actuator being in communication with both the first valvedevice and the second valve device, the actuator being configured tocause each valve device to open or close simultaneously, the accumulatorassisting in maintaining a generally constant pressure when the actuatorcauses each valve device to close.
 2. A system as defined in claim 1,wherein each valve device comprises an inner sleeve positioned within anouter sleeve, the inner sleeve being attached to the outer sleeve so asto define a discrete area, the discrete area being in fluidcommunication with the actuator wherein, when fluid is fed into thediscrete area, the discrete area inflates to form a balloon and causesthe restriction of blood flow through the arteriovenous graft, theaccumulator assisting in maintaining the discrete area in an inflatedstate until the fluid is removed from the discrete are.
 3. A system asdefined in claim 1, wherein the fluid injection port is in fluidcommunication with the first valve device and the second valve device.4. A system as defined in claim 3, wherein the fluid injection port isalso in fluid communication with the accumulator.
 5. A system as definedin claim 1, wherein the fluid injection port comprises a diaphragm, thediaphragm being of sufficient thickness to resist pressure from theaccumulator and prevent fluid from unintentionally leaking from thediaphragm.
 6. A system as defined in claim 1, wherein the accumulatorcomprises a spring and a piston housed within the first housing portion,the spring being configured to exert a force against the piston.
 7. Asystem as defined in claim 2, wherein, when inflated, the balloons ofeach valve device have a spherical or substantially spherical shape. 8.A system as defined in claim 2, wherein the outer sleeve of each valvedevice is more rigid than the inner sleeve and wherein the outer sleevemaintains its shape when the respective balloon is inflated.
 9. A systemas defined in claim 2, wherein the arteriovenous graft is positionedwithin the inner sleeve of the balloon of the first valve device and theballoon of the second valve device.
 10. A system as defined in claim 1,wherein the actuator is configured to deliver a fluid to each valvedevice for opening and closing the valve devices.
 11. A hemodialysismethod comprising: subcutaneously implanting an arteriovenous graftsystem in a patient, the arteriovenous graft system including anarteriovenous graft having a first end that is connected to an arteryand a second end that is connected to a vein, the arteriovenous graftsystem further including a first valve device positioned at the arterialend of the arteriovenous graft and a second valve device positioned atthe venous end of the arteriovenous graft, the arteriovenous graftsystem further including an actuator in communication with both thefirst valve device and the second valve device, the actuator including ahousing having a first housing portion and a second housing portionspaced apart from the first housing portion, the first housing portionconfigured to receive an accumulator of the actuator and the secondhousing portion configured to receive a fluid injection port of theactuator such that the accumulator is separate from the fluid injectionport; opening the first and second valve devices simultaneously usingthe actuator causing blood to flow through the arteriovenous graft;inserting first and second hypodermic needles into the arteriovenousgraft, the hypodermic needles being in fluid communication with ahemodialysis machine; circulating blood through the hemodialysismachine; and after a sufficient amount of blood has been circulatedthrough the hemodialysis machine, closing the first and second valvedevices using the actuator, the accumulator assisting in maintaining agenerally constant pressure when the first and second valve devices areclosed.
 12. A method as defined in claim 11, further comprising the stepof flushing the arteriovenous graft after the first and second valvedevices have been closed.
 13. A method as defined in claim 12, whereinthe arteriovenous graft is flushed by injecting a cleaning fluid intothe arteriovenous graft and then removing the fluid.
 14. A method asdefined in claim 11, wherein each valve device comprises an inner sleevepositioned within an outer sleeve, the inner sleeve being attached tothe outer sleeve so as to define a discrete area, the discrete areabeing in fluid communication with the actuator wherein, when fluid isfed into the discrete area, the discrete area inflates to form a balloonand causes the restriction of blood flow through the arteriovenousgraft, the accumulator assisting in maintaining the discrete area in aninflated state until the fluid is removed from the discrete are.
 15. Amethod as defined in claim 11, wherein the fluid injection port is influid communication with the first valve device and the second valvedevice.
 16. A method as defined in claim 14, wherein the fluid injectionport that is in fluid communication with the first valve device and thesecond valve device, the fluid injection port being positioned adjacentto the accumulator.
 17. A method as defined in claim 11, wherein thefluid injection port comprises a diaphragm, the diaphragm being ofsufficient thickness to resist pressure from the accumulator and preventfluid from unintentionally leaking from the diaphragm.
 18. A method asdefined in claim 13, wherein the accumulator comprises a spring and apiston housed within the first housing portion, the spring beingconfigured to exert a force against the piston.
 19. The system of claim6, wherein the accumulator further comprises a diaphragm positionedbetween the piston and a fluid path extending between the fluidinjection port and an outlet of the actuator.
 20. The method of claim18, wherein the accumulator further comprises a diaphragm positionedbetween the piston and a fluid path extending between the fluidinjection port and an outlet of the actuator.